Cellulosic and lignocellulosic feedstocks and wastes, such as agricultural residues, wood, forestry wastes, sludge from paper manufacture, and municipal and industrial solid wastes, provide a potentially large renewable feedstock for the production of valuable products such as fuels and other chemicals. Cellulosic and lignocellulosic feedstocks and wastes, composed of carbohydrate polymers comprising cellulose, hemicellulose, glucans and lignin are generally treated by a variety of chemical, mechanical and enzymatic means to release primarily hexose and pentose sugars, which can then be fermented to useful products.
First, biomass feedstocks are treated to make the carbohydrate polymers of cellulosic and lignocellulosic materials more readily available to saccharification enzymes, which is typically called pretreatment. The pretreated biomass is then further hydrolyzed in the presence of saccharification enzymes to release oligosaccharides and/or monosaccharides in a hydrolyzate. Saccharification enzymes used to produce fermentable sugars from pretreated biomass typically include one or more glycosidases, such as cellulose-hydrolyzing glycosidases, hemicellulose-hydrolyzing glycosidases, and starch-hydrolyzing glycosidases, as well as peptidases, lipases, ligninases and/or feruloyl esterases. Saccharification enzymes and methods for biomass treatment are reviewed in Lynd, L. R., et al. (Microbiol. Mol. Biol. Rev. (2002) 66:506-577).
During pretreatment of biomass, different components of cellulose, hemicellulose and lignin may be released that can include sugars and/or by-products, including compounds such as acetic acid, formic acid, levulinic acid, furaldehydes and phenolic compounds. Some of the by-products are inhibitors in that they affect the activities of saccharification enzymes and/or the growth and metabolism of microorganisms used in subsequent fermentation. These inhibitors can reduce the efficiencies of the saccharification and/or fermentation processes. Some attempts have been made to remove said inhibitors with additional steps, such as collection of sugars thereby creating a prehydrolyzate. These measures are unsatisfactory because they are not economical and result in reduced production of sugars.
Thus, there is a need for a pretreatment method that produces pretreated biomass having maximal retention of sugars and minimal presence of inhibitors, without forming a separate pretreatment sugar stream (prehydrolysate). This would provide a more economical and effective in-put biomass for use in saccharification followed by fermentation to produce useful products.